This invention relates generally to enclosures for electrical components and, more particularly, to a waterproof enclosure for electrical devices.
Enclosures are used in electrical power distribution systems to house various electrical components. These enclosures protect the electrical distribution equipment mounted therein from damage. Such applications include electrical switchboards, switchgear, and motor control centers. The degree of protection provided by the enclosure is dictated by the area in which the enclosure is to be located. The National Electrical Manufacturer""s Association (NEMA) defines different types of enclosures by the location of the enclosure and the various elements that the enclosure must be able to withstand. For example, NEMA Type 3 enclosures are for outdoor use, and NEMA Type 3R must provide a degree of protection agains falling rain, sleet, and external ice formation. Enclosures may also be designed to meet waterproof ratings as listed in Underwriters Laboratories standard 891 section 35 and ANSI/IEEE standard C37.20.3-1987 Section 5.2.9.
A typical outdoor enclosure (e.g., NEMA Type 3R) is shown in FIGS. 1 and 2. The switchboard type enclosure 10 includes a front frame 12 and a roof assembly 14 attached to a switchboard section 16. Switchboard section 16 is an indoor type enclosure (e.g., NEMA Type 1 and 2), which includes a metal cover secured to a frame 18 and forming side covers 20 and back cover 22. Mounted within switchboard section 16 are a plurality of electrical devices such as circuit breakers, fusible switches, motor controllers, or other electrical components (not shown). Front frame 12 is attached to the perimeter of the perimeter of the switchboard section 16. Front frame 12 includes walls 24 extending forward from side covers 20, and a door 26. Walls 24 and door 26 protect the electrical components within switchboard section 16 from the elements, while door 26 allows personnel to access these electrical devices. A handle 28 with provisions for a padlock prevent unauthorized access to the electrical devices. Roof assembly 14 includes a sloped hood 30 that extends across the width of switchboard section 16 from side 20 to side 20. Hood 30 extends a distance (shown here as five inches) past the back cover 22 of switchboard section 16 and past the front of door 26. Front and rear edges of hood 30 include flanges 32, 34 that extend downwardly. Secured between flange 32 and front frame 12 and between flange 34 and rear frame 16 are a pair of screen vents 36, which both extends across the width of hood 30. Typically, the screen vents 36 are formed of wire or foam filters to keep out water, debris, and insects. A pair of caps 38 are disposed along the edges of hood 30 adjacent sides 20, 24.
An exploded view of roof assembly 14 is shown in FIG. 3. Referring to FIGS. 2 and 3, hood 30 includes mounting flanges 50 which extend along sides of hood 30. Flanges 50 of hood are secured to lifting brackets 52. Lifting brackets 52 are secured to the frame 18 of switchboard section 16 and extend along the entire length of hood 30. Lifting brackets 52 provide a lifting point on enclosure 10 if it is necessary to move enclosure 10. Once enclosure 10 is in position, caps 38 are secured to flanges 50. An optional center lifting bracket 54 and center cap 56 are shown for use with switchboard sections 16 having a portion of the frame 18 extending through the center of the switchboard section 16.
The enclosure 10 shown in FIGS. 1-3 uses front and rear overhangs, formed by the extension of roof assembly 14 past back cover 22 and front of door 26, to vent heat from the electrical devices mounted within the enclosure. However, the rear overhang increases the area the customer must allocate to the equipment by adding, for example, five inches of depth between the back cover 22 of the equipment and any any object next to which one would place it.
In applications of the enclosure 10 of FIGS. 1-3, if a rear overhang cannot be used, the entire roof assembly must be shifted so that the flange 34 on the rear of hood 30 is flush with the back cover 22. However, this modification eliminates the convective flow of air through the enclosure 10. Indeed, in enclosures 10 where such a modification is made, the ampere rating of the enclosure must be reduced. In addition, this modification increases the amount of overhang on the front of the enclosure 10.
It is therefore desirable to provide an enclosure for electrical components having reduced space requirements through removal of the rear overhang, while providing sufficient ventilation to prevent overheating of the internal electrical components, and while meeting waterproof ratings listed in Underwriters Laboratories standard 891 section 35 and ANSI/IEEE standard C37.20.3-1987 Section 5.2.9.
In an exemplary embodiment of the invention, a roof assembly forms the top of an enclosure for electrical devices. The roof assembly includes a hood formed from a sheet of waterproof material. The hood extends across a portion of the top of the enclosure. A cap extends above a portion of the hood, and a channel extends between the cap and the hood. The channel allows the passage of air into and out of the enclosure.